This invention relates to a process of forming colored photographic images.
It is well known to etching-bleach the silver images. The silver complex diffusion transfer process (DTR process) and various applications of the process are also well known. The DTR process capable of forming silver images of high contrast, high resolution, and high density is applicable to the reproduction of documents, preparation of block copies, and the like. As one of known applications, there is described in Journal of Applied Photographic Engineering, Vol. 5, No. 3, pp. 171-172 (1979) a process for forming a colored image, wherein use is made of an image receptive material comprising a transparent film support and, provided thereon, an image receptive layer containing a pigment such as, for example, yellow, magenta, cyan, blue, red, or green one, and after the diffusion transfer development the silver image areas are etching-bleached, leaving behind colored image areas. The colored image thus obtained can be used in a poster, catalog, original for overhead projection, and overlay. Such a photographic material has already been on the market.
The disadvantage of the above process on the part of suppliers is the requirement of supplying the photographic materials in a large variety of colors; such a requirement cannot be met beyond a certain limit. The disadvantages on the part of consumers include the necessary stock of photographic materials in various colors; difficulty of selecting a desired color; uneconomical use of a plurarity of image receptive materials in combining pictures or letters of different colors; and impossibility of freely change the depth of color. Moreover, the colored image is not transferable to another image receptive sheet, because it is composed of a pigment. The transfer of colored image is very useful in combining or superposing different images to form various color images or in forming an image composed of developed silver and a color. The above disadvantages exist not only in the image receptive materials but also generally in common silver halide photosensitive materials.
The above-mentioned difficulties of the conventional process can be overcome by treating the silver image forming layer with a solution of a colorant capable of dyeing said layer at any stage such as, for example, after formation of silver image and before or after etching-bleach of the silver image. However, because it is a dye which colors the layer instead of a pigment in the conventional process, this method has several disadvantages such that owing to an insufficient affinity of the dye for gelatin, it is difficult to attain a sufficiently high color density and a sufficient dyeing speed even when a highly concentrated dye solution is used; when dyeing is carried out with different dyes, each dye diffuses to adjacent image areas, resulting in mixed color. Moreover, when a colored dye image is transferred to a substrate material, a dye staining tends to occur in the areas where the image transfer is not intended. Since the transfer is performed through the liquid medium, such staining seems to originate from the dye dissolved and diffused out of the colored image and from the dye dissolved and diffused out of the dye image which has been transferred to the substrate, both stainings occurring simultaneously under certain conditions of transfer. Another problem is the low density of transferred image, which can be increased to a certain extent by prolonging the time of transfer, which, however, accompanies an increase in staining.